The present invention relates generally to the field of air traffic display systems. More particularly, the invention includes a method and system for depicting an aircraft or a ground vehicle on a display using a target icon which is correlated to the integrity of the incoming data describing the vehicle""s position and track.
Since the dawn of aviation, pilots and aircraft designers alike have continually sought new and better ways to augment and enrich the pilot""s own sensory perception with a variety of on-board and ground-based equipment. For safe flight, pilots need information about the flight path and the environment in which his or her own ship is flying. Flight path data includes position, track, speed, and other navigational data, as well as a variety of information from the pilot""s ownship, as it is called. Environmental data includes information about the weather, the terrain, and the position and track of other aircraft in the vicinity.
The purpose of ownship equipment is to provide an aid to visual acquisition, conflict detection, threat assessment, and conflict avoidance. Advances in aviation technology have vastly increased the amount of information that can be provided to pilots. Multi-function cockpit displays such as a Cockpit Display of Traffic Information (CDTI) may depict a wide variety of data, such as air traffic, ground traffic, weather, and terrain, at different times and in different combinations, using a single screen.
The CDTI is a means of presenting surveillance information about the surrounding traffic to the flight crew. Traffic includes aircraft as well as ground vehicles or fixed obstructions. The information presented includes the relative position of a target of interest. The term xe2x80x9ctargetxe2x80x9d refers to traffic that is nearby the ownship and may be of interest to the flight crew and other CDTI users. Target data for the CDTI may be obtained from a variety of sources, including Automatic Dependent Surveillancexe2x80x94Broadcast (ADS-B). Targets typically are represented by displaying a selected icon on the CDTI.
One challenge presented by the wide variety of data available for display on a CDTI is the fact that different data may possess different levels of integrity. In this context, integrity is related to the probability that the true location of an aircraft is outside a certain volume of space defined by a containment boundary that surrounds the three-dimensional position being broadcast. A first aircraft, for example, may be broadcasting its three-dimensional position with high integrity, whereas the data being broadcast by a second aircraft may have much lower integrity. Displaying both aircraft with the same icon may create the false impression that the data supporting the position has equal integrity.
High-integrity air traffic data is desired for safe flight, especially given the increase in air traffic worldwide. The integrity of the data about a particular target depends on several factors, including the timeliness of the latest data transmission and the accuracy of the position data within the signal transmitted.
Different applications that make use of the traffic data on a CDTI require different levels of data integrity. Target data may be used and processed in a variety of applications including, for example, a Conflict Situational Awareness (CSA) application and a Range Monitoring (RM) application. Some applications require and use only traffic data having a sufficiently high integrity.
Target data integrity may also vary over time, depending on the characteristics of a particular transmission. Data signal quality can improve or degrade due to satellite positions, sensor positioning, or sporadic signal reception. In some instances, the integrity of the ownship""s position data may degrade, thereby affecting the ability of onboard applications to accurately monitor the traffic situation.
Thus, there is a need to raise the awareness of pilots and other users of air traffic monitoring data to the integrity of the data supporting a target being displayed. There is a related need to raise the awareness of pilots to changes in data integrity.
There is also a need for differentiating between high-integrity and lower-integrity target data to indicate which targets are suitable for use by a particular application.
There is still further a need for updating the traffic icon if and when the target data""s integrity changes.
The above and other needs are met by the present invention which, in one embodiment, provides a method for determining the integrity of incoming target data and provides a system for assigning and displaying a target icon that is correlated to reflect the target data""s integrity. In a preferred embodiment, the invention provides a set of target icons which are correlated to target data integrity. Such a set of icons should be capable of varying in color, size, shape, and/or other characteristics such as being outlined or filled, or flashing or still, to reflect the target data""s integrity.
It should be understood that integrity includes both an accuracy aspect and a timeliness aspect. Data from a target will not be assigned a high integrity unless it is both accurate and recent. Accurate position data must be recent to be reliable. Likewise, recent position data must also be accurate to be reliable. In one aspect of the invention, the system compares the current time to the time of measurement of the incoming position data.
Integrity is related to the probability that the true position of an aircraft is outside an imaginary volume of space (defined by a containment boundary) which surrounds the three-dimensional position being broadcast. If the probability that the true position is outside the containment boundary is high, then the data accuracy is low and, therefore, the integrity of the position data is low. Conversely, if the probability that the true position is outside the containment boundary is low, then the data accuracy is high and, accordingly, the integrity of the position data is high.
According to another aspect, the system of the present invention comprises a computer or other automated system for processing and implementing the rules described herein in order to display accurate and timely data on a cockpit display. In one preferred embodiment, the system itself is housed within a Link and Display Processor Unit (LDPU) which serves as the data link between the signals received and the icons displayed.
In one preferred embodiment, the system of the present invention is in communication with a plurality of signal receivers, an LDPU, and a Cockpit Display of Traffic Information (CDTI). Each signal receiver is configured to receive a particular type of signal and communicate the data received to the LDPU. One or more signal receivers may be housed within the LDPU itself. Through the signal receivers, position data is received about a plurality of targets.
The system of the present invention is capable of processing ADS-B signals broadcast by targets of interest and is also capable of interpreting other types of signals. An ADS-B (Automatic Dependent Surveillancexe2x80x94Broadcast) signal includes a variety of indicators, typically including a Type Code, a time of applicability, a pressure altitude, a latitude, and a longitude.
The Type Code indicates the type of message being broadcast and serves as an accuracy indicator of the data to follow. The Type Code may be used to determine a value for the Navigational Uncertainty Category for Position (NUCp). The NUCp value indicates a level of accuracy of the latitude and longitude coordinates included in the ADS-B position message. For a target broadcasting a transponder signal instead of an ADS-B signal, a Type Code may be calculated and then used to determine the NUCp value.
The time of applicability embedded within the ADS-B signal represents the time when the position measurement was made.
One aspect of the present invention includes a set of rules for determining the integrity of the data being received about a target. A target in this context is defined as traffic that is nearby the ownship and may be of interest to the user. Applying the rules to a set of measurable criteria determines whether the integrity of the target data is high or low. High-integrity targets are depicted on the cockpit display using a certain icon, while low-integrity targets are depicted using a different icon. In one embodiment, high-integrity targets are depicted using a pointed chevron, while low-integrity targets are depicted using a rounded bullet.
In another aspect of the present invention, applying the rules to determine integrity continues in time, displaying changes in the icon displayed which are intended to communicate changes in signal integrity. In other words, the data integrity is continually monitored for changes in order to provide current information to the user in the form of specific icons reflecting any change in data integrity. Changing the target icon alerts the flight crew to changes in data integrity. Changing the target icon also alerts the flight crew to the fact that a target may no longer be of sufficient integrity to be monitored by the conflict detection applications.
In one aspect of the present invention, each target is assigned a status. Target status is continually updated to reflect changes in status known as transition events. Target status is changed in response to a transition event if and when certain logic and timing constraints are satisfied. When target status changes, the system of the present invention changes the target icon used to display the target.
Target status begins with the xe2x80x9cAcquirexe2x80x9d state when the target data is first received, and ends with the xe2x80x9cDropxe2x80x9d state when the target data is lost. A variety of transition events may occur while a target is being monitored. In one aspect of the present invention, a specific target icon is used to represent each specific transition event in order to alert the user to changes in target status.
The target icons of the present invention are designed to convey the current target status and whether the target has undergone a transition event. In an important aspect of the present invention, each target icon also conveys the target""s position data integrity. A transition event associated with, or caused by, a change in position data integrity is of particular importance to pilots and other users of air traffic monitoring applications.
In one aspect of the present invention, when one of the signal receivers receives data from a new source, the system of the present invention assigns a target status of xe2x80x9cAcquirexe2x80x9d to identify the new target. The inventive system immediately analyzes the integrity of the data embedded within the new target signal, using certain logic and timing constraints, in order to assign the appropriate target icon.
Generally, if the target data integrity is high and the ownship""s data integrity is high, then the new high-integrity target is depicted using a pointed chevron icon. If, however, the target data integrity is low or the ownship""s data integrity is low, then the new low-integrity target is depicted using a rounded bullet icon. Airborne targets are cyan in color, while ground targets are tan in color.
More specifically, the integrity of the target""s position is determined by analyzing the data within the signal. The Type Code within an ADS-B signal is a first indicator of the accuracy of the data. In one aspect of the present invention, the Type Code is mapped to a particular value for the Navigational Uncertainty Category for Position (NUCp). The NUCp value indicates a level of integrity of the latitude and longitude coordinates included in the ADS-B position message. The NUCp value is defined as the radius of a circle in the horizontal plane (specifically, in the local plane tangent to the WGS-84 ellipsoid), with its center being at the true position of the target, which describes the region which is assured to contain the indicated horizontal position. The probability that the indicated position lies outside this circle is 1 times 10xe2x88x927 per flight hour. Because integrity is also affected by the timeliness of the data, the time of applicability embedded within the ADS-B signal is also used to determine data integrity.
In one preferred aspect of the invention, the integrity may be determined to be high if and when the following logic and timing constraints are satisfied: (1) the NUCp value indicates a horizontal containment radius of one nautical mile or less; (2) the ADS-B message includes valid position and velocity information; and, (3) the time of applicability, when compared to the current time, indicates that the most recent ADS-B message was received within the last five seconds. Targets not meeting these requirements are designated as having a lower level of integrity.
It should be understood that the values associated with the integrity analysis, such as the horizontal containment limit of one nautical mile and the time limit of five seconds, may in a preferred embodiment be adjusted by the user or by the system, depending upon the monitoring application to be executed against the target. For example, a Range Monitoring (RM) application may require a time limit of three seconds in order to accurately monitor a target of interest. The system of the present invention is preferably capable of adjusting the time limit to accommodate the needs of various applications.
In another aspect of the present invention, the user""s ownship position data integrity is also continuously monitored. Accurate ownship data is important to safe flight because it is compared to target data when determining whether a potential conflict between aircraft exists. Thus, if the ownship position data has a low level of integrity (poor quality and/or poor timeliness), then the targets are displayed with target icons representing a lower level of integrity. In one embodiment, the ownship is displayed using a white triangle icon. The color white is also typically used to display the ownship""s track, distance range markings, and airport reference identification codes.
Moreover, as described above, the determination of target data integrity also depends upon ownship data integrity. Ownship data integrity is important in the operating environment of the inventive system because an overall air traffic monitoring system may include conflict detection applications that compare target data to ownship data. In applications such as Conflict Situational Awareness (CSA) and Range Monitoring (RM), the results of the internal conflict detection algorithms are not sufficiently reliable unless the target data has high integrity and the ownship data has high integrity.
In a related aspect of the system of the present invention, the target icon may change in response to a change in ownship data integrity. Displaying target icons that also reflect ownship data integrity is an important tool for pilots and other users because, in practice, they are relying on the accuracy of the conflict detection algorithms for safe flight.
It should be understood, however, that the present invention may be utilized not only where the ownship is an aircraft aloft or on the ground, but also where the ownship is a ground vehicle, a stationary monitoring station, or another fixed location. Of course, the data describing a fixed ownship location would typically have a high integrity.
In another aspect of the present invention, the system continuously monitors target data integrity and target status. An important transition event affecting data integrity is the loss or degradation of an incoming target signal. In one embodiment of the inventive system, the target icon changes if and when target data integrity degrades for a period of five seconds (or when ownship data integrity degrades for a period of five seconds). For example, in one preferred embodiment, an airborne high-integrity target displayed by a cyan chevron would change to a cyan bullet icon in response to a data integrity degrade.
In another aspect of the invention, a change of target icon may be accompanied by an audible alert message. For example, when target integrity degrades, an audible alert such as xe2x80x9cTarget Degradexe2x80x9d may be sounded to alert the user (in addition to and associated with the change in the shape of the target icon from a chevron to a bullet). Similarly, in a related aspect of the invention, a change of target icon may also be accompanied by a text message on the screen. For example, when target integrity degrades, a text message such as xe2x80x9cTarget Degradexe2x80x9d or xe2x80x9cTGT Degradexe2x80x9d may be displayed to alert the user.
Likewise, the re-acquisition or improvement of a target signal is sensed by the inventive system. In one embodiment of the inventive system, the target icon changes if target data integrity improves and has not degraded for a period of three seconds; provided, however, that ownship data integrity has either improved or has not degraded for a period of three seconds and no conflict alert condition has existed for more than two seconds.
It should be understood that the inventive system of changing the target icon in response to changes in data integrity may be used in an overall system of air traffic monitoring and conflict detection that necessarily involves changes in target icons that are unrelated to data integrity. For example, the pilot in certain monitoring systems may select or de-select a particular target on the display to learn more about its status. In one system, for example, the target icon color is changed to green and the target icon shape becomes filled when the target has been xe2x80x9cselectedxe2x80x9d by the user. While the target icon may change in response to being selected or de-selected, this change does not reflect a change in data integrity.
Also, the starting and stopping of certain conflict detection applications such as CSA and RM, in certain systems, may also involved a change in the target icon displayed. In one such system, for example, the target icon color is changed to yellow and the target icon flashes while a conflict detection application is being applied against a target.
Furthermore, changes in target icon may occur in certain systems when a conflict detection application is being applied against a target that has also been xe2x80x9cselectedxe2x80x9d by the user. In one such system, for example, the target icon color is changed to yellow, the target icon shape becomes filled, and the target icon flashes while a conflict detection application is being applied against a xe2x80x9cselectedxe2x80x9d target.
Finally, it should be understood that the target icon is typically removed from the display when a target signal is lost for a period of time.
In an important aspect of the present invention, the system of changing target icons in correlation with changes in data integrity is further designed to work in concert with other traffic monitoring systems without creating confusion or delivering misleading information about data integrity. The target icon attributes in a preferred embodiment of the invention consist of shapes, sizes, colors, and/or other icon conditions that complement the standardized target icon attributes already in use to depict targets of interest.
According to another aspect of the present invention, for targets on the ground, surface vehicles may be shown using a tan square icon. Aircraft on the ground may be shown using a tan chevron, markedly smaller than the chevron used for airborne aircraft. When the position data from a ground target is not valid, then the target may be displayed using a tan circle icon. Stationary ground targets such as tethered pole towers may be shown using a tan caret icon.
According to another aspect of the present invention, the criteria used to determine the integrity of incoming target data may be adjusted either manually by the user or automatically by a different air traffic monitoring application. In one preferred embodiment, the upper and lower limits applied to any element within the incoming signal, such as the Type Code or the horizontal containment limit or the time limit, may be adjusted to accommodate the needs of the particular application.
Thus, embodiments of the present invention provide a method for determining the integrity of incoming target data and a system for assigning and displaying a target icon correlated to the target data integrity. Embodiments of the present invention further provide a method for adjusting the criteria against which incoming target data is measured for integrity. Embodiments of the present invention further provide a method and system for determining when a target signal undergoes a transition of sufficient magnitude to warrant a change in the cockpit display. Embodiments of the present invention provide a method and system for changing the target icon when and if the target data integrity changes. Thus, embodiments of the present invention provide distinct advantages in displaying correlated target icons on a cockpit display.